Whitepaper is mandatory for all ICO, except the company is cocacola or apple. As long as it is genuine,investors may not care because of their track record but we might just want to know how the token/blockchain might be relevant and useful
ICO usually is a new project and whitepaper is mandatory. Without it, no investors will be interested to join. It will different if the project that offers ICO is a well known and already well established company.